E-ISSN: 2278–179X JECET; June – August-2013; Vol.2.No.3, 677-684.

Journal of Environmental Science, Computer Science and Engineering & Technology An International Peer Review E-3 Journal of Sciences and Technology

Available online at www.jecet.org Engineering & Technology Research Article

A Comparative Analysis of Firing Angle Based Speed Control Scheme of DC Motor Ranjana Khandare, Pritam Kumar and Asutosh Kumar Pandey Rishiraj Institute of Technology, Indore [M.P] India Received: 3 July 2013; Revised: 20 July 2013; Accepted: 26 July 2013

Abstract: The speed control scheme of DC motor and provides a comparative analysis of firing angle based speed control technique. The best control characteristics of DC motor have used in industries for different rang of loading condition. A dual converter comprised of two single phase AC-DC thyristor converter is proposed. Speed of DC motor is controlled by controlling the armature voltage. Armature voltage is controlled using AC-DC converter. This paper also describe the circulating operation of dual converter, in which rectifier 1 will be rectifying (0‹ αA‹900) and rectifier 2 will be inverting (900‹αB‹1800). The linear & non-linear regions are clearly visible in control characteristics. Firing control scheme improve armature voltage & also reduce ripple content & possibility of discontinuous conduction in circuit. The controlled performance exhibited is superior & also firing angle smoothly controlled with fast response. The dual converter simulation is done in MATLAB. Key words: AC-DC converter, DC motor, speed control.

INTRODUCTION The motion plays an important role in industries. The production process of varies industries different for require speed profile. DC drives are widely used due to high starting, acceleration & retarding torques. Also the speed control of DC motor is simpler & less costly compare to other drive. DC JECET; June – August 2013; Vol.2.No.3, 677-684.

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drives are widely used in rolling mills, machine tools, cutting tools, overhead cranes and other industries application which require large starting torque. DC machine is highly versatile & flexible machine. They also employ in many cutting application such as actuators & speed or sensors that is DC motor are very versatile for the purpose of speed control. The aim of this paper is describe the principle of dc motor speed control using armature voltage control method.In armature control mode the field current held constant & adjustable voltage applied to the armature. This paper provides a comparative technique for different firing based speed control. Simulation models of DC motor, speed control method for DC motor drive have developed using MATLAB/Simulink.

MODELING OF DC MOTOR The versatile control characteristics of separately excited DC motor shows the dynamic & steady state model. The schematic representation of separately excited DC motor is shown in figure.

Fig.1: Equvivalent circuit of separately excited DC motor Where, Va is applied voltage of DC motor &Eb back emf in circuit & A-AA,F-FF are armature and field connection across armature & field in Figure 1. General equation of dc motor for steady state representation. The basic equation is

& Eb is given by

Also the torque

T = KeфIa The greatest advantages of DC motor are smooth speed control. Parameter Va ,Ra ,ф control the speed. Following are the methods of speed control of DC motor. 1/ Armature voltage control 2/ Field flux control JECET; June – August 2013; Vol.2.No.3, 677-684..

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3/ Armature resistance control Generally armature voltage control is preferred because of high efficiency, good transient response & good speed regulation & also it provide speed control below base speed, because of armature voltage cannot be allowed to exceed rated value. For speed control above base speed the field flux control method is used.

Also, 1.

αV

2.

α 1/ф

3.

Adjusting armature voltage or field current will change the motor speed.

In case of armature resistance control, speed is control using external resistance connected in series with armature circuit i.e. wasting of power. So this method is not used. Speed control scheme is Proposed based on thyristraised dual converter. General purpose microprocessor based control circuit for single phase dual converter. The performance exhibited is superior & also firing angle is smoothly controlled with fast response.

Fig.2: Single phase dual converter drive In proposed scheme, a converter system is used of DC motor. A pulse generator is used for firing angle control of converter design. The thyristor of converter receive conduction the firing pulse either mode of continuous or discontinuous operation. To simplify single phase dual converter, two of these full converter are connected back to back as shown in figure 2. The system will provide four quadrant operations & is called a dual converter. Dual converter are normally used in high power variable JECET; June – August 2013; Vol.2.No.3, 677-684..

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speed drive. Delay αA & αB are angle of converter 1 & 2 respectively & corresponding average output voltage are V1 & V2 . The delay angle is controlled such that one converter operates as a rectifier & other converter operates as an inverter, but both converter produce same average output voltage. The average output voltage of converter 1 operates with firing angle αa (0‹ αA‹900) & similarly average output voltage of converter 2 operates with firing angle αb . (900‹αB‹1800) Also ,if firing pulse of converter are controlled , so that αA + αB = 1800 For achieving the average DC voltage of two converters are equal to one another. For speed reversal αA is increased and αB is decreased to satisfy above equation .The motor back emf exceeds the magnitude of V1 & V2 .The armature current shift to rectifier 2 & motor operates in second quadrant. The current is controlled & adjust the firing angle αA & αB continuously, so as to break the motor at maxi. Allowable current for initial speed to zero & then accelerates to the desired speed in reverse direction. The power rating up to around 10 KW single phase fully controlled rectifier can be used.

SIMULATION To observe the effect of armature voltage on torque speed curve four different firing angles are used with the voltage applied to the field circuit kept constant 150 V. A constant 240 V, 50 HZs , AC supply is applied to input of single phase dual converter. The different output voltage & current are obtained on armature of motor. When firing angle are 300 &1500, 600 & 1200 , 1200 & 600, 1500 & 300 The average value of output voltage can be controlled by controlling or changing the firing angle α Armature voltage with firing angle of rectifier1 300 & rectifier2 1500 for single phase dual converter. Simulink model of armature voltage speed control method using single phase dual converter

Fig. 3: Armature voltage with firing angle of rectifier1 300 & rectifier2 1500 for single phase dual converter.

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Rated Power (P) Rated Armature Voltage Armature Resistance Ra Armature Inductance La Field Resistance Field Inductance Rated Speed Rated Field Voltage

5HP 240V 0.78Ω 0.016H Rf 150Ω Lf 112.5H 1750RPM 150V

Fig. 4: Armature voltage with firing angle of rectifier1 600 & rectifier2 1200 for single phase dual converter Speed, armature current, field current &electrical torque at 50N.m

Fig.5: Armature voltage with firing angle of rectifier1 1200 & rectifier2 600 for single phase dual converter

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Fig.6: Speed, armature current, field current &electrical torque at 100N.m

Fig. 7: Armature voltage with firing angle of rectifier 1 1500 & rectifier 2 300 for single phase dual converter.

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Fig. 8: Speed, armature current, field current &electrical torque at 100N.m. are also shown in fig.7

Fig. 9: Speed, armature current, field current &electrical torque at 500N.m. Simulink model used to get armature voltage & current & also torque speed characteristics for different firing angle are shown in above figure. The figure shows linearity & nonlinearity in torque speed curve. Non- linearity because of discontinuous of armature current. When the firing angle increases the non- linearity also increases. The figure shows the continuous discontinuous operation in dual converter. JECET; June – August 2013; Vol.2.No.3, 677-684..

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CONCLUSION This paper present speed control of separately excited DC motor using single phase dual converter. A firing scheme for single phase fully controlled dual converter is described & built. The scheme utilise the same circuit for both rectification & regeneration mode of operation. Different torque speed curve are obtained for more range of loading condition. Linear & non- linear region are clearly seen in torque speed characteristics. This paper provides a comparative analysis for different firing angle control scheme. A four quadrant speed control DC drive fed from the proposed dual converter is designed and obtained results shown to be in good interact with experimentally theory. An optimize & efficient method of speed control can be develop. An experiment on DC drive can be developing for UG student for their understanding.

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*Corresponding Author: Asutosh Kumar Pandey; Rishiraj Institute of Technology, Indore (M.P.) India .

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